3.8. Vulnerability Dependency

Fast spreading worms, such as W32/CodeRed, Linux/Slapper, W32/Blaster, or Solaris/Sadmind, can only infect a new host if the system can be exploited via a known vulnerability. If the system is not vulnerable or is already patched, such worms cannot infect them. However, several worms, such as W32/Welchia, exploits multiple vulnerabilities to invade new systems. Therefore, the system might remain exploitable by at least one of the nonpatched vulnerabilities.